The present invention relates to a process for producing a Schottky diode, particularly of the type comprising an epitaxial layer supporting an oxide layer, a metal layer establishing the Schottky contact and a metal guard ring.
In the field of semiconductor components it is known to use, particularly in detection or mixer high-frequency circuits, Schottky diodes formed by a contact of a metal with a weakly doped semiconductor which presents rectifying properties. However a disadvantage of such diodes resides in the fact that in numerous applications their voltage behaviour is an important limiting factor.
In FIG. 1, accompanying the present application, there is shown a schematical sectional view of a Schottky diode formed at the level of a monocrystalline n-type silicon layer 2 and on the top of which is disposed a metal layer 3. Reference 4 designates the silicon oxide layer SiO.sub.2. Now the region 1, which forms the space charge zone, possesses, at the level of the periphery of the diode, a small radius of curvature and there results therefrom a high electric field which frequently causes premature breakdown of the diode. This field and the current in the diode are also very sensitive to surface effects.
In the prior art, a first solution shown in FIG. 2 accompanying the present application, consisted in using a guard ring 5 formed by diffusion, of type p, in the case of n-type silicon. In FIG. 2, the same references have been kept as those in FIG. 1 to designate similar elements. In this case, the result obtained is an extension of the space charge zone 6, with a more rounded shape at the edges of the Schottky diode, which improves the voltage behavior, but from a certain level a current finishes by flowing in the parasite junction diode formed by the guard ring and which may store charge carriers under certain conditions of polarization, and the result is a high switching time.
It was then proposed (FIG. 3), to avoid any storage of minority carriers and to eliminate the passage of the parasite current, to put in place two guard rings 7, 8 one of n.sup.+ type the other of p.sup.+ type, forming two junctions disposed head-to-tail. This arrangement certainly increases the extent of the space charge zone, which takes on the shape 9, but, apart from the fact that this solution is fairly complex, it causes the increase in the area of the element, which is detrimental to obtaining a high integration density of the circuits.
Finally another solution was proposed according to which an improvement in voltage behavior is obtained by means of a metal guard ring 10 (FIG. 4) deposited on the chamfered periphery of the oxide SiO.sub.2 4. By giving this ring 10 a special shape, such as shown, the electric field is reduced at the edges of the diode, which improves the voltage behavior. The space charge zone is designated in this case by the reference 11. Nevertheless, it turns out that the results depend on the profile of the guard ring and that the limitation comes from the periphery.
In the three known solutions for improving the voltage behavior of Schottky diodes, this voltage behavior remains however mediocre in quality; the characteristic of the diode is far from being ideal and there is associated therewith, furthermore, in the first two known solutions, parasite elements of the capacity, storage diode type, etc.